On Thu, Jul 14, 2016 at 09:51:53AM +0100, Mel Gorman wrote: > On Thu, Jul 14, 2016 at 10:11:19AM +0900, Minchan Kim wrote: > > > The patch means that the vmstat accounting and tracepoint data is also > > > out of sync. One thing I wanted to be able to do was > > > > > > 1. Observe that there are alloc stalls on DMA32 or some other low zone > > > 2. Activate mm_vmscan_direct_reclaim_begin, filter on classzone_idx == > > > DMA32 and identify the source of the lowmem allocations > > > > > > If your patch is applied, I cannot depend on the stall stats any more > > > and the tracepoint is required to determine if there really any > > > zone-contrained allocations. It can be *inferred* from the skip stats > > > but only if such skips occurred and that is not guaranteed. > > > > Just a nit: > > > > Hmm, can't we omit classzone_idx in mm_vm_scan_direct_begin_template? > > Because every functions already have gfp_flags so that we can classzone_idx > > via gfp_zone(gfp_flags) without passing it. > > > > We could but it's potentially wrong. classzone_idx *should* be derived > from the gfp_flags but it's possible a bug would lead it to be another > value. The saving from passing it in is marginal at best. > > If it's omitted from the tracepoint itself, there is a small amount of > disk saving which is potentially significant if there is a lot of direct > reclaim. Unfortunately, it also makes it harder to filter that > tracepoint because the filter rules must be an implementation of > gfp_zone. > > Right now I believe the saving is marginal and the cost of potentially > using the wrong information or making the filtering harder offsets that > marginal saving. Agreed. Thanks. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>